A spindle unit used for miniature motors and miniature rotors has been hitherto formed as shown in FIG. 21.
That is to say, a pair of radial ball bearings 21 and 22 are arranged above and below on the outer periphery of a shaft 20, a cylindrical spacer 23 is arranged between the respective outer races 21a and 22a of these radial ball bearings 21 and 22 to determine the respective positions of the radial ball bearings 21 and 22 with each other, the radial ball bearings 21 and 22 and the cylindrical spacer 23 are fixed within a hole H in a bearing housing 24 and such rotor 25 as a pulley, disk or turntable is fixed to the end part of the shaft 20 to rotate the shaft 20 side.
However, in the spindle unit of the above mentioned construction, in order to prevent dust or the like from entering the radial ball bearings 21 and 22 and reducing the performance, there has been used a so-called double sealing structure wherein sealing members S are arranged on both sides of balls 21c provided within the radial ball bearings. These radial ball bearings 21 and 22 have defects that they have many component parts, are complicated to assemble and are therefore high in the cost.
A rotary mechanism using the above mentioned marketed conventional radial ball bearings 21 and 22 is of a structure wherein balls 21c and 22c are contained respectively in the clearances between the inner races 21b and 22b and outer races 21a and 22a and has defects that the numbers and diameters of the balls 21c and 22c are predetermined and the balls can not be increased in the diameter, number and rigidity as required.